1. Field of the Invention
The invention pertains to molecular imprinting of small particles and, more particularly, to a method of molecular imprinting which utilizes a propellant as the solvent and dispersing agent of the matrix material and to imprinted particles formed by the method as well as devices coated with imprinted particles, such as, for example, surface acoustic wave (SAW) devices. In addition, the invention pertains to a method for the formation of small particles of monomers containing solid-state reactivity.
2. Description of the Prior Art
Molecular imprinting is a process, which involves arranging of polymerizable functional monomers around a template (print) molecule. This is achieved either by utilizing non-covalent interactions such as hydrogen bonds, ion-pair interactions, etc. (non-covalent imprinting), or by reversible covalent interactions (covalent imprinting) between the print molecule and the functional monomers. Typically, a molecule to be imprinted (template) is combined with a mixture of functionalized and non-functionalized monomers so that the monomers surround the template. In the process, functionalized monomers align themselves in a binding relationship to complementary functional groups on the template to form therefore a complex with the template. After polymerization, functional groups are held in position by the highly cross-linked polymeric matrix. The template is then removed, and the resulting material contains imprinted binding sites which are complimentary in size and shape to the template. The complementary binding groups, arising from the functionalized polymer groups incorporated during the imprinting, are specifically positioned to enhance the preferential substrate binding and, if desired, subsequent catalysis. The imprinted polymer materials are capable of specific sorption or specific catalytic activity. A good description of state of the art of molecular imprinting can be found in Mosbach, K., Trends in Biochemical Sciences, Vol. 7, pp. 92-96, 1994; Wulff, G., Trends in Biotechnology, Vol. 11, pp. 85-87, 1993; and Andersson, et al., Molecular Interactions in Bioseparations (Ngo. T. T. ed.), pp. 383-394.
The functionalized monomers usually used for molecular imprinting are: acrylic acids [Anderson, L.; Sellergren, B; Mosbach, K Tetrahedron Lett. 1984, 25, p.5211. Sellergren, B.; Lepisto, M.; Mosbach, K. J. Am. Chem. Soc. 1988, 110, p.5853. Andersson, L. I.; Mosbach, K. J. Chromatogr. 1990, 516, p.313. Matsui, J.; Miyoshi, Y.; Takeuchi, T. Chem. Lett. 1995, p.1007.], vinylbenzoic acids [Andersson, L.; Sellergren, B.; Mosbach, K. Tetrahedron Lett. 1984, 25, p.5211], acrylamino-sulfonic acids [Dunkin, 1. R.; Lenfeld, J.; Sherrington, D. C. Polymer 1993, 34, p.77], amino-metacrylamides [Beach, J. V.; Shea, K. J. J. Am. Chem. Soc. 1994, 116, p.379.], vinylpyridines [Ramstrom, O.; Andersson, L. I.; Mosbach, K. J. Org Chem. 1993, 58, p.7562. Kempe, M.; Fischer, L.; Mosbach, K. J. Mol. Recognit. 1993, 6, p.25], vinyl imidozales [Kempe, M.; Fischer, L.; Mosbach, K. J. Mol. Recognit. 1993, Vol. 6, p.25. Leonhardt, A.; Mosbach, K. React. Polym. 1987, 6, p.285.], acrylamides [Yu, C.; Mosbach, K. J. Org Chem. 1997, 62, p.4057.], and vinyl-iminodiacetic acids [Dhal, P. K.; Arnold, F. H. J. Am. Chem. Soc. 1991, 113, p.7417. Kempe, M.; Glad, M.; Mosbach, K. J. Mol. Recognit 1995, 8, p.35.].
Prior to this invention, methods of molecular imprinting have achieved only modest success in the enhancing polymer selectivity and catalytic activity. The reason for this is, that in order to be effective in a wide scale, imprinted materials must have binding/active sites to be homogeneous (in specificity and activity), be well formed (based on shape and reactivity), and be easily accessible by the reactant molecules (access is affected by shape, size and polarity of the channels leading to the catalytic site). The imprinted polymeric materials created by prior art methodologies have sites that are generally not very accessible and not homogenous, as they often have different binding affinities and/or reactivities. These problems mainly arise from the method used for producing the imprinted polymer particles.
A common method of molecular imprinting is referred to as solution polymerization. This method results in the formation of imprinted sites that are completely encased within the polymer. In order to enable an access to those sites, the polymer monolith must be subjected to mechanically grinding to produce particles that have exposed sites. Grinding produces irregularly shaped particles and typically only less than 50 percent (50%) of the ground polymer is recovered as useable particles with size less than 25 xcexcm. Irregular particles generally give less efficient devices mainly because of the deformation of a large number of the binding sites. As a result, damage to the sites adversely affects their selectivity and activity. An alternative method to increase accessibility to the imprinted sites is by the use of porogen compounds which are known to generate foam-like polymer structures when combined with polymer forming materials. Porogens, which are typically inert solvents, are mixed with the polymerizable monomers during the imprinting process and are washed away after polymerization is complete. This creates large pores that allow access to the created binding sites. However, while the porogens are removed, some of the structural integrity of the polymer can be lost at the same time, leading to the deformation of the sites and loss in specificity and activity.
Another alternative for molecular imprinting is by direct polymerization of particles in liquid media. Surfactants are used to create molecular microstructures, such as micelles or reverse micelles. Then, inorganic or organic monomers are polymerized around those molecular microstructures at the surfactant-solvent interface to form polymer beads, dispersed in the liquid media to prevent agglomeration. The size and shape of the formed beads highly depend on the chemistry of the mixture and reaction conditions, such as temperature and stirring. When the surfactant is removed, the remaining material has a size and shape complementary to the size and shape of the initial molecular microstructures. By controlling variables such as surfactant selection and concentration, a variety of different microstructure shapes such as micellar, cubic, tetragonal, lamellar, tubular and reverse micellar can be formed. Consequently, monodisperse particles of a variety of different sizes and porous materials with a variety of different shapes of pores and channels can be created. Methods of making porous material are described, for example, in the following patents each of which are incorporated herein by reference: U.S. Pat. No. 5,250,282 to Kresge et al; U.S. Pat. No. 5,304,363 to Beck et al; U.S. Pat. No. 5,321,102 to Loy et al; U.S. Pat. No. 5,538,710 to Guo et al; U.S. Pat. No. 5,622,684 to Pennavaia et al; U.S. Pat. No. 5,750,085 to Yamada.
Molecular imprinting by direct polymerization of particles in liquid media is more advantageous, but still has limitations due to the liquid media needed to disperse particles to prevent particles agglomeration. Therefore, after polymerization, particles need to be separated from the liquid media for further use, which is not an easy task, especially for small particles. While in many applications, imprinted polymers should be deposited on the special surfaces, such as in chemical and biological sensors, and in chromatography and filtration devices. Deposition of the imprinted polymer material and adherence on the surface remains a big problem.
U.S. Pat. No. 5,587,273 to Yan et al., which is herein incorporated by reference, describes a way of molecular imprinting of polymer film directly on the surface of sensor. The invention describes molecularly imprinted substrate and sensors employing the imprinted substrate for detecting the presence or absence of analytes. One embodiment of the invention comprises first forming a solution comprising a solvent and (a) a polymeric material capable of undergoing an addition reaction with a nitrene, (b) a crosslinking agent (c) a functionalizing monomer and (d) an imprinting molecule. A silicon wafer is then spin coated with the solution. The solvent is evaporated to form a film on the silicon wafer. The film is exposed to an energy source to crosslink the substrate, and the imprinting molecule is then extracted from the film. Described method is an advance in deposition of imprinted polymers to the sensing surfaces. But there is no solution disclosed in the literature for imprinting of polymer particles directly on the surfaces of devices. Prior researchers have focussed on the preparation of imprinted particles, but not on attachment of the particles to the surfaces of device, and it would be advantageous to have a methodology which allowed direct attachment of imprinted particles to substrate surfaces.
Aerosol and vapor technology has been used for many industrial and medicinal applications which utilize particles. An aerosol is a two-phase system consisting of a gaseous continuous phase and a discontinuous phase of individual particles. The individual particles in an aerosol can be solids or liquids (Swift, D. L. (1985), xe2x80x9cAerosol characterization and generation,xe2x80x9d in Aerosols in Medicine Principles, Diagnosis and Therapy (Moren, F. et al. eds) 53-75). Supercritical fluids have been used in the production of aerosols for precipitation of fine solid particles. The phenomenon was first observed and documented as early as 1879 and was described the precipitation of solids from supercritical fluids (Hannay, J. B. and Hogarth, J., On the Solubility of Solids in Gases, Proc. Roy. Soc. London, 1879, A29, 324). The sudden reduction in pressure reduces the solvent power of the supercritical fluid, causing precipitation of the solute as fine particles. This phenomenon has been exploited in many processes for producing fine particles, using co-solvents (Sievers, et al. PCT Publication WO 9317665 published Sep. 16, 1993, Donsi, G. and Reverchon, E. (1991), xe2x80x9cMicronization by Means of Supercritical Fluids: Possibility of Application to Pharmaceutical Field,xe2x80x9d Pharm. Acta Helv. 66:170-173), anti-solvents (Debenedetti, P. G., et al. (1993), xe2x80x9cApplication of supercritical fluids for the production of sustained delivery devices,xe2x80x9d J. Controlled Release 24:27-44, PCT Publication WO 90/03782 of The Upjohn Company for xe2x80x9cFinely Divided Solid Crystalline Powders via Precipitation Into an Anti-Solventxe2x80x9d, Yeo, S-D, et al. (1993), xe2x80x9cFormation of Microparticulate Protein Powders Using a Supercritical Fluid Antisolvent,xe2x80x9d Biotechnology and Bioengineering 41:341-346), as well as pure supercritical solvents (Mohamed, R. S., et al. (1988), xe2x80x9cSolids Formation After the Expansion of Supercritical Mixtures,xe2x80x9d in Supercritical Fluid Science and Technology, Johnston, K. P. and Penninger, J. M. L., eds., Tom, J. W. and Debenedetti, P. B. (1991), xe2x80x9cParticle Formation with Supercritical Fluidsxe2x80x94a Review,xe2x80x9d J. Aerosol. Sci. 22:555-584, Smith U.S. Pat. No. 4,582,731 for xe2x80x9cSupercritical Fluid Molecular Spray Film Deposition and Powder Formation,xe2x80x9d issued Apr. 15, 1986, and Smith U.S. Pat. No. 4,734,451 for xe2x80x9cSupercritical Fluid Molecular Spray Thin Films and Fine Powders). In the processes described, fine aerosols comprising the desired substance are formed by mixing a nongaseous pressurized or/and supercritical fluid(s) with the desired substance, which is present in a solution, dispersion, suspension, micellar system or emulsion. During rapid reduction of the pressure on composition the pressurized/supercritical fluids form a gas and a gas-borne dispersion of fine particles, liquid or solid.
There are many acronyms associated with those processes, including RESS, GAS or SAS, SEDS, ASES, and PGSS (Jennifer Jung, Michel Perrut Particle design using supercritical fluids: Literature and patent survey Journal of Supercritical Fluids 20 (2001) 179-219). RESS refers to Rapid Expansion of Supercritical Solutions. This process contemplates dissolving the product in the fluid and rapidly depressurizing this solution through a nozzle, causing an extremely rapid nucleation of the product into a highly dispersed material. GAS or SAS is Gas (or Supercritical fluid) Anti-Solvent, one specific implementation being SEDS (Solution Enhanced Dispersion by Supercritical Fluids). The general concept contemplates decreasing the solvent power of a polar liquid solvent in which the substrate is dissolved, by saturating it with carbon dioxide in supercritical conditions, causing substrate precipitation or re-crystallization. ASES is used when micro- or nano-particles are expected. The process contemplates pulverizing a solution of the substrate(s) in an organic solvent into a vessel swept by a supercritical fluid. SEDS is a specific implementation of ASES wherein there is co-pulverizing of the substrate(s) solution and a stream of supercritical carbon dioxide through nozzles. PGSS stands for Particles from Gas-Saturated Solutions (or Suspensions). The process includes dissolving a supercritical fluid into a liquid substrate, or a solution of the substrate(s) in a solvent, or a suspension of the substrate(s) in a solvent followed by a rapid depressurization of this mixture through a nozzle causing the formation of solid particles or liquid droplets.
Development of microspheres/capsules, containing a load of needed ingredient, is one of the most rapidly developing area in medicine, food industry, agrochemicals, cosmetics. Many efficient drugs have been reformulated to allow control of delivery location and rate, the active substance being distributed directly to the target to enhance the treatment efficiency and reduce the doses and related side effects. Some of the researchers classify particles/capsules smaller than 1 xcexcm as nanoparticles and those larger than 1000 xcexcm as macro-particles. Commercial particles/capsules typically have a diameter between 3 and 800 xcexcm and contain 10-90 wt. % of carrier material. A wide range of materials have been embedded/encapsulated in microspheres/capsules, including adhesives, agrochemicals, live cells, active enzymes (W. Fischer, B. Muller, Patent EP 0 322 687, Dec. 17, 1988; P. Debenedetti, J. W. Tom, S. D. Yeo, G. B. Lim, Application of Supercritical Fluids for the Production of Sustained Delivery Devices. Journal of Controlled Release, 24, 1993, 27-44; L. Frederiksen, K. Anton, B. J. Barrat, P. Van Hoogevest, H. Leuenberger. Proceedings of the 3 rd International Symposium on Supercritical Fluids; Tome 3; G. Brunner, M. Perrut (Eds.), ISBN 2-905-267-23-8, 17-19 October, Strasbourg, 1994, 235-240; M. Hanna, P. York, Patent WO 95/01221, 1994; M. Hanna, P. York, Patent WO 96/00610, 1995; K. Mishima, S. Yamaguchi, H. Umemoto, Patent JP 8-104830, 1996; P. Pallado, L. Benedetti, L. Callegaro, Patent WO 96/29998, 1996; W. Majewski, M. Perrut, Patent FR 99.12005, 27 September). Despite these advances, there are few materials which include an active agent embedded or encapsulated in a carrier matrix (or otherwise associated with the matrix) which are specifically designed for targeted delivery of the active agent to a particular site. It would be advantageous for example, if a material were available where a drug or toxin were associated with a slow release matrix material, wherein the material could be targeted for delivery to a tissue, organ or other site of activity, and then have slow sustained release at the targeted site. Prior to this invention, no such delivery material having each of these attributes existed.
There are several method of handling materials with solid state reactivity to develop small particles of reacted solid materials. There is a need to produce small particles which retain reactivity in the solid state. Reprecipitation in liquid solvents is one of the techniques used (Application: JP 92-238160 19920907 to Kasai; Oikawa H; Oshikiri T; Kasai H; Okada S; Tripathy SK; Nakanishi H. Various types of polydiacetylene microcrystals fabricated by reprecipitation technique and some applications. POLYMERS FOR ADVANCED TECHNOLOGIES 2000, Vol 11, Iss 8-12, pp 783-790). The process is carried out by dissolving an organic material in a solvent, adding poor solvent, followed by crystallization or polymerization of the microcrystals to form particles. Adding 4-BCMU in EtOH solvents to water dropwise and irradiating with high-pressure Hg lamp gave polydiacetylene particles showing average diameter 100-200 nm. The reprecipitation method is a useful technique to fabricate organic microcrystals such as polydiacetylene (PDA), low-molecular-weight aromatic compounds, organic functional dyes that have features located in a mesoscopic phase between a single molecule and bulk crystals, and organic microcrystals which are expected to exhibit peculiar optical and electronic properties.
One known variation involves recrystallization in supercritical fluid by change of temperature and addition of anti solvents (Kasai, Hitoshi; Okazaki, Susumu; Okada, Shuji; Oikawa, Hidetoshi; Adschiri, Tadafumi; Arai, Kunio; Nakanishi, Hachiro. Fabrication of organic microcrystals by supercritical fluid crystallization method and their optical properties. MCLC SandT, Sect. B: Nonlinear Opt. (2000), 24(1-2), 83-88; Komai, Y; Kasai, H; Hirakoso, H; Hakuta, Y; Okada, S; Oikawa, H; Adschiri, T; Inomata, H; Arai, K; Nakanishi, H. Section 3: Thin Films - Size and Form Control of Titanylphthalocyanine Microcrystals by Supercritical Fluid Crystallization Method. Molecular Crystals and Liquid Crystals, 1998, v.322, p.167, 6p). This method involves the use of solvents which makes the particles thus produced only accessible in or subject to the solvent as an impurity. It would be advantageous to have particles and particle producing methods where both agglomeration and solvent impurities are completely avoided.
It is an object of the invention to provide an improved method of fabricating molecularly imprinted polymeric particles which can selectively bind specific compounds or classes of compounds.
It is another object of the invention to provide polymeric particles which are molecularly imprinted, and which are capable of substantially improved performance over prior art materials made by different methodologies.
It is yet another object of the invention to provide devices which are used for highly selective binding of molecules or classes of molecules, which are coated with molecularly imprinted polymeric materials, such as for example SAW devices and other sensors, chromatography devices and filters, and purification devices of all types (e.g., cigarette filters, water filters, etc.).
It is still another object of the invention to provide a new and improved method of making micron and less than micron sized particles from compounds that have solid-state reactivity, with or without molecular imprinting.
According to the invention, particles are created from a mixture of propellant and desired substance which is present in the form of solution, dispersion, suspension, micellar system or emulsion; which comprises at least one polymerizable monomer. A xe2x80x9cpropellantxe2x80x9d is a compressed gas or mixture under elevated pressure, where at least one of the components of the mixture may be a supercritical fluid, and, while expanded, propellant dispenses the contents of the mixture to form particles. The term xe2x80x9cparticlexe2x80x9d as used herein refers to both solid particles and liquid droplets. As the mixture passes through a capillary nozzle or other orifice, the mixture undergoes fast expansion so as to create fine particles of the mixture, containing monomer, that are preferably less than 100 microns in size, and most preferably less than 50 microns in size. In one embodiment, the particles include polymerizable monomers with or without cross-linking agents, and an initiating species (e.g., activators which initiate polymerization or cross-linking (or both processes)). In another embodiment, the monomers themselves exhibit solid-state reactivity, meaning that they change from a solid monomer to a solid polymer without a change of the material physical state. This second embodiment can be used to make particles of substantially uniform, small size, which can be molecularly imprinted or not be molecularly imprinted, and constitutes a new manner of handling materials with solid state reactivity. These particles are advantageous in that they are not agglomerated, and do not require a solvent. In addition, they are stable for long periods of time (e.g., 1-10 years) and can be selectively polymerized at any desired time. The particles formed from solid state reactivity monomers can have wide ranging applications including in the formation of coatings on surfaces and in optical data storage.
For molecular imprinting, in either embodiment, a template can be combined with the mixture either before expansion or after particle formation. A template is used for imprinting the polymeric material, and can be any molecule which is selectively releasable from a polymer formed from the monomers in the particle. In many applications, it is preferable that the template does not covalently bond to the polymer which is formed. However, in some applications, the template may be released by hydrolyzing bonds or changing the ionic attraction between a template molecule and the polymer matrix. In molecular imprinting, the template needs to be extracted from the polymer particle after polymerization of the monomer or monomer mixture in the particle formed by expansion. The template can be a chemical or biological compound or substrate (a portion of a biological or chemical compound, or a biological entity). The choice of template will depend on the application planned for the molecularly imprinted polymer particle. Specifically, the template may be a compound (e.g., toxin, carcinogen, or any compound of interest, etc.) that one would like to sense in a gaseous or fluid environment, or a compound which is to be removed from a gaseous or fluid environment by selective binding to the molecular imprint site such as by a filter or other separation device. The invention may also have application in biology or biotechnology. In some cases antigens or enzymes of interest could serve as the template molecule, and then the imprinted polymer particles would be able to selectively bind the specific biological entities. Otherwise, the molecular imprinting can produce the artificial enzymes and antibodies.
However, it should be understood that the imprint can be designed to selectively bind, sorb, or otherwise associate with more than a single compound, which served as the template compound. Specifically, the imprinting process may allow the molecularly imprinted polymer particle to bind any molecule that has a size (spatial size) and/or arrangement of chemical functional groups which is substantially the same as said template. This should be especially useful in the preparation of imprinted polymer particles that may be used, for example, in detection or sorption of chemical and biological warfare agents. Specifically, compounds, which have a size and arrangement of chemical functional groups that are similar to nerve gas agents, or other chemical weapons, but which are not themselves potent substances, may be used to molecularly imprint polymer materials that can then be used to bind, sorb or otherwise associate with the dangerous substances. In this way, the molecularly imprinted materials might be fabricated in a manner which would be more safe than working with the dangerous substances themselves.
If the template is added to the mixture prior to expansion, the distribution of the imprinted sites within the polymer particles is virtually assured. This is because the propellant will solubilize and/or disperse both the matrix forming compounds (i.e. the monomers) and the template to form a homogenous mixture, and after the expansion the particles are formed that contain matrix compounds and template evenly dispersed therein.
If the template is added to the mixture after expansion, the template must be diffused into the particles. This can be done in either the gas or liquid phase using a suitable carrier. Even distribution of the imprinted sites on the surface of the polymer particles may be achieved using this technique because particles are formed with substantially uniform surface representation. The imprinted sites are readily accessible, as the particles surfaces are exposed to the analyte.
The propellant in the mixture being expanded can be 20-99.99% by weight of the entire mixture to be expanded. The mixture, containing at least one monomer, be they monomers having a solid state reactivity, or a mixture of monomers, crosslinkers and initiators, can be 80-0.01% by weight of the entire mixture. If the template is added to the mixture to be expanded, the template can comprise 1-30.00% by weight of the mixture.
This is the first time it has been shown that propellant can be effectively used as a solvent or distribution agent in the formation of molecular imprinting in micron and submicron sized particles. In particular, it is the first time that a propellant has been used for development of micron and submicron sized particles from materials with solid state reactivity. The propellant is maintained in a fluid state under pressure, but, when pressure is relieved, it instantly transitions to a gaseous state. This allows the propellant to be immediately separated from the monomers that will ultimately form the polymer particle not containing impurities due to the propellant. The propellant may advantageously be a supercritical fluid or may include as at least one component a supercritical fluid. The supercritical fluid can solubilize the monomers in the mixture which is to be expanded, and then, after expansion, will leave the particles thus formed as a gas. Examples of propellants which can be used in the practice of this invention include, but not limited to, chlorofluorocarbons (freons), hydrofluorocarbons, alkanes, alkenes, noble gases (e.g., helium and argon), nitrogen, sulfur hexafluoride, fluorocarbons, nitrous oxide, hydrogen, ammonia, carbon monoxide and carbon dioxide.
The ratio of the propellant and monomers in the mixture to be expanded can be adjusted to achieve the formation of particles of varying sizes. Likewise, the nozzle opening can be adjusted to control particle size. The choice of system pressure and temperature can be experimentally optimized and depends on the type of materials to be expanded, monomers, and propellant. The propellant could also be a mixture of more than one material. For example, two different gases might be used, or a supercritical fluid and another compound might be used.
A particularly advantageous aspect of this invention is to produce the molecularly imprinted particles or simply the small particles formed from materials of solid-state reactivity. Particles formed by expansion of a mixture containing propellant and solid state reactivity monomers will not agglomerate, and will be free of solvent, and are stable for long periods of time (1-10 years). These particles can be polymerized into solid particles without a change in the physical state of the material. Thus, these particles may deposited onto surfaces where desired (e.g., on sensors, optical devices), at a desired time, and be selectively polymerized at any time after formation of the particle.
A two step polymerization can be performed in one embodiment of this invention which is particularly advantageous for securing imprinted or non-imprinted particles directly on the surface of a substrate. In the first step, a stream of particles emanating at the site of expansion is subjected to an energy source sufficient to cause an initial polymerization of the monomer while particles are in flight towards a deposition surface or other collection location. This can be performed by radiant energy, such as ultraviolet, gamma radiation, infrared radiation, intense light in the visible spectrum, etc. Alternatively, heat can be used for specific monomers. The purpose of the initial polymerization is to allow some of the polymerization or crosslinking to begin. It is preferable that the initial polymerization is sufficient to make the particles more viscous such that there physical morphology begins to be established. The amount of energy applied will depend on the materials in the composite particle containing monomers and template, the size of the particle, whether or not initiators are present in the particle, the time of flight, and other factors. In the second step, the particles (which are now partially polymerized particles containing template material) are deposited onto a surface of the support, such as a SAW device, chromatography support, or filter, where they are subjected to more energy (e.g., heat or radiant energy) to fully polymerize the particle matrix directly on the surface of the support. This allows the particle to mechanically and/or chemically adhere to the surface of the support without having significant changes in its morphology of the particle. Specifically, the outer surface is fairly solidified in the initial polymerization, however, upon deposition onto a support, a portion of the particle containing monomers would then be polymerizable in the final polymerization step. This monomeric portion may also be selected to chemically interact with functional groups on the support surface. Alternatively, the impact onto the support surface will wedge some of the monomers into cavities and depressions on the surface, whereupon the final polymerization step will assure a mechanical bond of the polymer particle within these cavities and depressions on the surface of the support. Thus, the polymeric particles of this invention are chemically or mechanically attached to the substrate without using an adhering agent or requiring a separate step to achieve good adherence. At the same time the method enables uniform distribution of particles on the support surface.
Alternatively, the particles could simply be collected in a collection container and subjected to the energy sufficient to fully polymerize or xe2x80x9ccurexe2x80x9d the particles.
The procedure assures that the imprinted small particles of substantially uniform size are formed. The invented procedures of molecular imprinting of polymer particles avoid deformation of the imprint sites by excluding grinding and solvent separation, enables uniform distribution of the imprinted sites, and increases their accessibility to analyte. After formation of the polymeric particles, the template compound is extracted by exposing the polymer particles to excess propellant/other supercritical fluid, or by any other means suitable for displacing the template from the polymeric particle.